1. Field of the Invention
This invention relates to a grinding head assembly characterized by an improved backing plate for mounting a grinding wheel, typically used to remove surface corrugations in railroad tracks.
2. Description of the Prior Art
Routine maintenance of railroad tracks includes grinding the surface of the rail to remove corrugations to restore a smooth, regular travel surface. Corrugations result from prolonged passage of rail cars over the rails, especially at curves. Elsewhere, corrugations appear in association with defective joints.
It is usual to pass a grinding machine which has longitudinally spaced multiple grinding heads over each rail. Generally, each grinding head has a grinding wheel attached to a holder. The holder is attached to a vertically disposed rotatable drive shaft which is driven by a motor. The grinding head is lowered until the plane surface of the grinding wheel is in contact with the surface of the rail. The head is rotated, creating a grinding motion on the surface of the rail, and the machine is moved along the railroad track to continuously grind lengths of the rail surface as the grinding head passes over it.
Grinding heads are typically rotated at 3600 rpm. It is essential that the holder and grinding wheel withstand the stresses associated with rotation at such a speed. In the prior art the effect of grinding stresses has been reduced by constructing a holder of multiple sections. This multiple section construction increases production and installation costs. There is a need in the art for a wheel holder of simple design that provides the rigidity necessary to withstand rotational stress while keeping cost of production and installation at a minimum.
Because of the rotational speed and associated centrifugal stresses, the component parts of the grinding head must be balanced if the head is to perform correctly. To achieve this, the wheel holder and grinding wheel must be accurately centered with respect to the axis of the drive shaft, the wheel holder, and with respect to each other. Two prior art patents disclose means to center the backing plate on the backing plate holder. Spencer (U.S. Pat. No. 1,079,304) and Panetti (U.S. Pat. No. 4,292,768) each disclose backing plates which are formed to mate and register coaxially with backing plate holders. The Panetti design is more complex than the Spencer design, but in Spencer as well as Panetti both the backing plate and backing plate holder must be specially cast, increasing production costs. In the Panetti design seating and centering of the backing plate is inconvenient because of the need to interlock two fairly complex surfaces under low visibility conditions. Even with the Spencer design a person installing or replacing the backing plate might anticipate some difficulty in seating and centering the plate on the holder. There is therefore a need for a simple and effective method to ensure automatic centering of the backing plate to diminish the time and cost of installation and replacement, and to reduce the cost of production.
Grinding wheels have been fastened to backing plates in the prior art by molding the wheel to the plate and by attaching the wheel to the plate with adhesive or nuts and bolts. If the wheel is molded to the plate, centering can be achieved by rotation of the backing plate during the molding process. Other centering means are needed if the wheel is to be attached by adhesive. Applicant knows of no prior art addressing that problem. There is therefore a need for a centering means that ensures that the grinding wheel is co-axially positioned relative to the backing plate so that the wheel-plate combination is in balance.
The process of installation and replacement of the component parts of a grinding head is complicated by their size and weight. There is danger of personal injury in handling bulky, heavy objects and the time involved in assembly or service is increased by the difficulty in handling the parts.
Panetti discloses a grinding head design that attempts to alleviate some of the difficulty in installation. A metal backing plate 7, integral with a grinding wheel 6, has notches 14, the edges of which engage retaining studs 16 on a support flange 1, to hold the assembly in place for clamping.
However, as has already been pointed out, the complex backing plate in Panetti must be interlocked with the complex backing plate holder, while their two surfaces are not visible to the installer, before the holding facility created by the stud and notch design can be utilized. Also, once the backing plate and grinding wheel are held in place their attachment to the backing plate holder is achieved by an additional component, a central clamping flange 9 which is held on the drive shaft by a screw 10. This flange and screw must be completely removed before a replacement wheel and backing plate can be installed. Thus, despite the facility of holding the wheel and backing plate combination during clamping, installation and replacement continues to be time-consuming and physically difficult.
There is therefore a need for grinding head components that can be easily and rapidly installed and serviced with minimal disassembly, for both safety and economic reasons.
Economics also requires maximum use from each component of the grinding head, particularly the grinding wheel. Thus, the design of the head should permit use of the abrasive material of the grinding wheel to the maximum extent or depth possible.